There is an excellent article in the New Yorker about Hilary Mantel's Wolf Hall and its sequel Bring up the Bodies (due out here in just a few days' time). James Wood puts his finger on where the author's gifts lie, and any novelist would do well to take note of the points he makes, I think.
"She knows that what gives fiction its vitality is not the accurate detail but the animate one, and that novelists are creators, not coroners, of the human case."
"... when a historical fact is central to a novelistic detail, Mantel uses it in a way so novelistically intelligent that the historical fact seems to have been secretly transposed into a fictional one ..."
"[she] has made a third category of the reality, the plausibly hypothetical. It’s what Aristotle claimed was the difference between the historian and the poet: the former describes what happened, and the latter what might happen."
"If you want to know what novelistic intelligence is, you might compare a page or two of Hilary Mantel’s work with worthy historical fiction by contemporary writers such as Peter Ackroyd or Susan Sontag. They are intelligent, but they are not novelistically intelligent. They copy the motions but rarely inhabit the movement of vitality. Mantel knows what to select, how to make her scenes vivid, how to kindle her characters. She seems almost incapable of abstraction or fraudulence; she instinctively grabs for the reachably real. Her two most recent novels concern famous historical events—Henry VIII’s divorce from Catherine of Aragon, his marriage to Anne Boleyn, her execution at the King’s orders, the English split from the Roman Church and the authority of the Pope—but they make the stories fragile again, with everything at suspenseful risk."